The present invention relates to canisters that prevent fuel vapor from leaking out of fuel tanks.
Canisters are used to prevent vaporized fuel (fuel vapor) from leaking out of fuel tanks into the atmosphere. A typical canister has a container filled with an adsorbent such as activated carbon to collect vapor. The container includes a vapor passage, a purging passage, and an air passage. Fuel vapor is drawn into the canister through the vapor passage. The fuel vapor is then purged toward an engine intake manifold through the purging passage. The air passage is used to draw atmospheric air into the canister or to release the air in the canister into the atmosphere. The adsorbent temporarily collects the fuel vapor drawn into the container from the fuel tank. The collected fuel is then separated from the adsorbent by the negative pressure, or vacuum pressure, produced during the operation of the engine and drawn into the purging passage toward the engine intake system (i.e., surge tank). Subsequently, the vapor drawn into the intake system is mixed with ambient air and sent to combustion chambers of the engine.
Fuel vapor also leaks out of fuel tank filler necks into the atmosphere during refueling. It is known that such fuel vapor is one factor that causes air pollution. Japanese Unexamined Patent Publication No. 8-210530 describes a canister having an onboard refueling vapor recovery function (ORVR) for solving this problem. The ORVR instantaneously collects a large amount of the vapor produced in a fuel tank during refueling. A breather passage is provided between the canister and the fuel tank in addition to the purge passage. The diameter of the breather passage is greater than that of the purge passage. The large amount of fuel vapor produced during refueling is collected in the canister by way of the breather passage. The canister incorporating the OCRV function collects the vapor in the fuel tank without leakage of the fuel vapor.
A canister having an ORVR function and located in the vicinity of an automobile fuel tank is shown in FIGS. 9(a), 9(b), and 9(c). As shown in the drawings, a box-like canister 101 includes a tank valve 104, which is located on a side wall of the canister 101 (left wall as shown in FIG. 9(b)), a tank port 103, a breather passage 112, a purge passage 114, and an atmospheric valve 130.
The canister 101 contains an adsorbent (activated carbon pellets) 125 for temporarily adsorbing fuel vapor. As shown in FIG. 9(b), a partition 118 separates the adsorbent 125 into two sections. The two sections of the adsorbent 125 are held between filters 123, 124. The partition 118 and the filters 123, 124 define first and second adsorbent compartments 119, 120 in the canister 101, while dispersion compartments 140, 141, 142 are defined at the ends of the adsorbent compartments 119, 120. The dispersion compartments 140, 141 function to disperse the fuel vapor moving through the canister 101 in a uniform manner such that localized concentration of the vapor does not take place.
The tank valve 104, the tank port 103, the breather passage 112, and the purge passage 114 are employed to adjust the pressure in a fuel tank 102 and are connected to the dispersion compartment 140, which communicates with the first adsorbent compartment 119 through the filter 123. The atmospheric valve 130 is connected with the dispersion compartment 142, which communicates with the second adsorbent compartment 120. The first and second adsorbent compartments 119, 120 communicate with each other through the filter 124 and the dispersion compartment 141.
The fuel vapor produced in the fuel tank 102 is normally drawn into the dispersion compartment 140 by way of the tank port 103 and the tank valve 104. When refueling the fuel tank 102, fuel vapor is drawn into the dispersion compartment 140 mainly through the breather passage 112. The fuel vapor drawn into the canister 101 passes through the filter 123 to be collected by the activated carbon in the first and second adsorbent compartments 119, 120.
When purging the fuel vapor, the negative pressure, or vacuum pressure, produced in the engine intake manifold (not shown) separates the fuel vapor from the activated carbon and draws the vapor into the intake manifold through the purge passage 114. The atmospheric valve 130 is a diaphragm type valve and has a relief port 131 for releasing the air in the canister 101 into the atmosphere and an intake port 132 for drawing the air into the canister 101. The intake port 132 is connected with an intake passage 155. When purging the fuel vapor in the canister 101, the low pressure, or negative pressure, in the dispersion compartment 140 is communicated to the intake port 132 thereby opening the intake port 132.
For immediate and efficient adsorption of a large amount of vapor during the employment of the ORVR function, it is preferable that the fuel vapor be uniformly dispersed when reaching the adsorbent 125. In the prior art canister 101, fuel vapor is dispersed to a certain degree in the dispersion compartment 140 to enhance the adsorbing rate of the fuel vapor by the activated carbon.
A large amount of fuel vapor having a high velocity is sent from the fuel tank 102 into the canister 101 through the breather passage 112. Furthermore, the diameter of the breather passage 112 is normally larger than that of the purge passage 114 and other passages to reduce the air flow resistance. Therefore, the breather passage 112 cannot be arranged freely. More specifically, the arrangement of the breather passage 112 in the prior art is limited to the end portion of the canister side wall.
Accordingly, it is difficult to obtain the desirable dispersion effects with the dispersion compartment 140. To solve this problem, the volume of the dispersion compartment 140 may be increased. However, this would enlarge the canister. A larger canister takes up valuable space in the automobile.